Recently, a magnetic random access memory (MRAM) that uses a tunneling magnetoresistive (TMR) effect has been developed. A magnetoresistive element that includes a magnetic tunnel junction (MTJ) is used for the magnetic random access memory, and this element has a high magnetoresistance change. A currently studied spin injection writing method uses an in-plane magnetization MTJ film and a perpendicular magnetization MTJ film, and allows the miniaturization of the structure of the magnetoresistive element and the reduction of a current. As an MTJ structure, a nonmagnetic layer serving as, for example, a tunnel barrier layer is made of, for example, MgO, and interfacial magnetic layers located on both sides of the tunnel barrier layer are made of CoFeB. In this case, a tunnel current value (resistance value) varies depending on whether the directions of perpendicular magnetization in the CoFeB layers are parallel or antiparallel. A high magnetoresistance (MR) ratio which represents the ratio between the parallel and antiparallel states is obtained.
The tunneling characteristics of an MTJ element depend on the crystallinity and crystalline orientation of the nonmagnetic layer and the interfacial magnetic layers after heat-treated to form a tunnel barrier structure.
However, there are a large number of factors that affect the crystallinity and crystalline orientation of the nonmagnetic layer and the interfacial magnetic layers; for example, the influence from the crystalline orientation of a bottom layer, the deterioration of the crystallinity of the interfacial magnetic layers attributed to element diffusion, and the change of crystallinity attributed to B (boron) element diffusion from the interfacial magnetic layers. It has therefore been not easy to provide a stably operating MTJ element.